Monocrotaline (MCT) is a natural product which induces pulmonary medial thickening and pulmonary hypertension in rats and monkeys. Because of similarities in the pathology, MCT-induced pulmonary hypertension has been suggested as a model for human primary pulmonary hypertension. Little is known about the mechanisms by which MCT or its toxic metabolite (MCTP) affect the pulmonary vasculature and induce pulmonary hypertension. This study will examine the responses of isolated pulmonary vascular cell types in culture to MCTP treatment. The first phase will involve establishing cultures of pulmonary artery endothelial cells, smooth muscle cells and fibroblasts, then determining which cells are affected by MCTP exposure and characterizing the extent and duration of MCTP-induced effects. Injury will be evaluated by monitoring cell detachment, permeability changes, cell lysis and morphological changes. Metabolic effects will be assessed by measuring ornithine decarboxylase activity, 3H-thymidine incorporation, and 5-hydroxytryptamine uptake after MCTP exposure. The second phase of this project will use the in vitro exposure system to study potential mechanisms by which MCTP could be stimulating pulmonary hypertension in vivo. The first hypothesis to be tested is that MCTP stimulates hypertrophy and/or hyperplasia of pulmonary vascular cells is directly. This will be explored by examining the effects of MCTP on cell DNA content, size and number. The second possibility to be tested is that MCTP stimulates hypertrophy and/or hyperplasia indirectly by inducing growth factor production by the injured pulmonary vascular cells. This will be explored by testing conditioned media from MCTP exposed cells for growth promoting activity, followed by characterization of the factor(s) responsible. These in vitro studies will provide the first information on the specific cellular responses of individual pulmonary vascular cell types to MCTP-induced injury and or allow mechanistic studies which are not yet possible in vivo. Ultimately, these studies of basic cellular mechanisms and interactions in the control of vascular wall thickness may suggest new approaches for diagnosis and therapy of pulmonary vascular disease.